Smart cards and smart card modules have been known for a long time. For example, in DE 195 00 925 A1, a smart card module is described including a substrate on which a semiconductor chip and metallic connecting pads are arranged, with the semiconductor chip being connected to the connecting pads via bonding wires. The semiconductor chip and the bonding wires are surrounded by an encapsulation compound. The semiconductor chip and the metallic connecting pads are arranged on one surface of the substrate. The contact surfaces for contact data interchange with the smart card are located on the other surface of the substrate. Access openings to the contact surfaces are cut out in the substrate. This smart card module is fit in a smart card by being inserted into the opening that is provided there and being adhesively bonded to the card body.
The general procedure for manufacture of smart card modules such as the type described above is for the semiconductor chips to be fixed by their active upper surfaces to a mount tape with their active upper surfaces pointing upward. The semiconductor chips are generally fixed on the mount tape by adhesive bonding. The mount tape has metallic surfaces at appropriate points, whose lower surface is used later to make contact between the smart card module and the peripherals. The contact between the connecting pads on the active upper surfaces of the semiconductor chips and these contact surfaces is made by of a wire bonding technique.
The wire bonding method has the major disadvantage that the use of bonding wires restricts to a large degree the miniaturization of the smart card module. It is not possible to achieve smart card modules with very small physical heights, since the bonding wires have a physical extent which cannot be undershot.
An alternative embodiment for a smart card module is also described in DE 195 00 925 A1, in which the contact surfaces and connecting pads are formed by a leadframe on which the semiconductor chip is arranged directly. The semiconductor chip is electrically and conductively fixed by its connecting pads by flip-chip contact-making directly on the corresponding contact surfaces and the connecting pads. This embodiment is a so-called “chip scale package”. “Chip scale packaging” is often also referred to by the abbreviation as “CSP”. In the case of CSP, which is a sub-type of flip-chip technology, interconnects are drawn directly on the active upper surface of the semiconductor chips, and solder balls, which facilitate the mounting of the semiconductor chip on a substrate, are then applied directly to these interconnects.
However, one major disadvantage of CSP technology is that the available active upper surface of the semiconductor chip generally does not offer sufficient area to produce all of the necessary external contacts. Furthermore, CSP technology is unsuitable for the manufacture of smart card modules because the semiconductor chips which are used in smart card modules are subject to significant miniaturization, that is to say to an extremely major “shrink”.
Processing of smart card microcontrollers using CSP technology for production of smart card modules, as proposed in DE 195 00 925 A1, therefore does not appear to be a feasible solution.